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It depends somewhat on what you mean by "find" -- if the end result of 'finding' is the phrase "they are the primitive eighth roots of unity", is that good enough?
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HurkylDec 22 '12 at 13:44

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You get this factorization almost instantaneously if you know that multiplication by a non-zero complex number consists of rotating and dilating. Use that to find fourth roots of $-1$.
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Michael HardyDec 22 '12 at 20:16

Yes, those answers are much better and more welcoming. This just smacks an answer to the question, which is technically correct, but the techniques it relies on are not explained at all.
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akkkkDec 22 '12 at 13:16